Method and device for filling a cavity with mortar

ABSTRACT

The invention concerns a method which consists in mixing the mortar and a setting and hardening accelerator in a screw conveyor ( 13 ) and in pouring into the cavity ( 8 ) by gravity the resulting mixture through a chute ( 14, 28, 30).

The present invention relates to a method and device for filling cavities, such as holes or trenches, particularly in infrastructure works, such as street pavements or roadways, sidewalks, etc.

It is known that work intended for maintaining such infrastructure works or for the maintenance and construction of networks of electrical cables, gas or water pipelines, etc. buried under these works, requires the digging of cavities which cause a nuisance to the users of these works. It is therefore essential to fill these cavities quickly, so that said works can be put into service again as quickly as possible after the end of said work has been carried out.

For this purpose, one idea has already been to fill these cavities with an ultrafast-setting mortar making it possible, for example, to put a road pavement into service again at most two hours after the end of this work. To achieve this, a cement-based mortar ready for use and manufactured in a specialized factory, usually called a concrete plant, is delivered by means of transport vehicles of the truck mixer type, and a setting and hardening accelerator for said mortar, in the form of powder and generally based on calcium aluminates, is added in said mixer, before said mortar is used in order to fill said cavities. However, this process has numerous disadvantages:

-   -   from the point of view of work safety: an operator has to climb         onto the rear of the truck mixer as far as the mouth of said         mixer, at the same time carrying bags of setting and hardening         accelerator product, weighing 25 kg or even 50 kg, and he has to         open said bags and empty their contents into the mixer. This         results in a risk of falling and exposure to the accelerator         dust;     -   from the point of view of the uniformity of the mortar: the         setting and hardening accelerator added to a full load of mortar         in the mixer cannot be mixed satisfactorily with the latter         during the rotation of said mixer, so that the setting and         hardening acceleration effect is not uniform over the entire         load of mortar. To remedy such a shortcoming, it is possible not         to fill the mixer with a full load of mortar, but this then         results in a high extra cost in logistic terms;     -   from the point of view of the rapidity of the setting and         hardening of the mortar; the setting and hardening of a cement         mortar which are accelerated by means of a calcium aluminate are         very rapid and are a function of the proportions, of the type of         cement and of the temperature. Consequently, if the emptying of         the mixer cannot be carried out immediately and quickly, the         mortar risks hardening in said mixer, making the latter useless.         Moreover, if the emptying of the mixer is immediate and quick,         but if the mortar cannot be used instantaneously, for example         due to the type of filling process, the mortar hardens before it         can be used to fill the cavities. This latter case arises         particularly when a plurality of small individual cavities or         narrow cavities, such as a trench of small width, are to be         filled;     -   from the point of view of the soiling of the mixer: after the         emptying of the mixer, a mortar layer always remains, which         adheres to the internal blades of the mixer. This mortar layer         hardens before the mixer truck is returned to the plant and it         has been possible to clean it, and a new layer will be added         during the next delivery.

The soiling of the mixer may become excessive within a single delivery day and require cleaning with a pneumatic hammer;

-   -   from the point of view of the contamination of the mixer load:         if the mixer truck is not carefully cleaned before being loaded         again, the remaining mortar may have an undesirable accelerator         effect on the new mortar load; and     -   from the point of view of the execution of a construction site:         since the setting and hardening of the water are very rapid         after the addition of the accelerator, the latter can be         introduced into the mixer only when the truck is in place and         ready to be unloaded. Then, however, since the introduction of         the accelerator into the mixer and the mixing of the mortar and         of the accelerator as a result of the rotation of said mixer         takes several minutes, this results in an irreducible waiting         time for all the operators, with a momentary interruption in         work on the construction site.

The object of the present invention is to overcome all these disadvantages.

For this purpose, according to the invention, the method for filling a cavity with a mortar capable of setting, at least one setting and hardening accelerator having to be added to a said mortar, and said mortar being available at the unloading orifice of a transport vehicle delivering it into the vicinity of said cavity, is notable in that:

-   -   a first flux is formed, consisting of said mortar and being         displaced in the direction of said cavity;     -   a second flux is formed, consisting of said setting and         hardening accelerator and being displaced in the direction of         said first flux;     -   said first and second fluxes are amalgamated by being mixed,         into a third flux; and     -   said third flux is introduced by gravity into said cavity.

Thus, by virtue of the present invention, the continuous addition and mixing of the setting and hardening accelerator with the mortar can be carried out outside the mixer of the transport vehicle, after the unloading of the ready-to-use mortar and just before the mortar with accelerated setting and hardening is placed into said cavity. All the disadvantages of the prior art recalled above are thus avoided.

Preferably, in order to obtain a desired setting time and hardening speed for the accelerated mortar filling the cavity, the flow rate of said second flux is adjusted as a function of the flow rate of said first flux in order to fix the proportion of setting and hardening accelerator in said third flux.

Excellent results have been obtained when said mortar is based on Portland cement, while the setting and hardening accelerator is based on calcium aluminates. The desired acceleration may also be obtained with other types of accelerators.

Advantageously, the Portland cement is of the CEM1 type, and its formula does not comprise mineral additives, such as fly ash or filler. It is possible, however, to obtain an acceptable result with cements of other types and in the presence of mineral additives.

The efficiency of the setting and hardening accelerator is a function of its mineralogy, and it has been observed that a reduced content of C₁₂A₇ (less than 1%) is preferable. The high-alumina cement known commercially under the reference LSR 5000 is an excellent setting and hardening accelerator.

This setting and hardening accelerator may take the form either of a powder or of a liquid, for example a slurry. In such a slurry, the calcium aluminate particles are in suspension in water, with calcium aluminate setting inhibitors and, optionally, dispersants. Inhibitors may be zinc borate, boric acid or citric acid, and they are incorporated into the calcium aluminates in proportions therein between 0.1% and 3% of the weight of calcium aluminates. The dispersants may be either of those known commercially under the references SPE 9413, PE 56-1 or Premia 150 and used in proportions therein from 0.1% to 3% of the weight of calcium aluminates. In this case, the setting. inhibitors, with or without dispersants, have the particular feature of providing suspensions highly stable in time, making it possible for them to be stored and transported for a relatively long period of time which amounts to several months, with suitable dosages. The dispersants, which are not indispensible, afford an increase in stability and viscosity which facilitate handling, in particular by pumping. This type of slurry has the advantage, when the slurry is mixed with a ready-to-use mortar, of accelerating the setting and hardening of the mixture, the acceleration inhibitor being deactivated simply as a result of contact with the mortar based on Portland cement, which deactivates it completely and thus allows the desired setting and hardening acceleration.

For the quality of the mixture and the speed of implementation, it is often preferable for the setting and hardening accelerator to take the form of slurry, rather than that of powder.

Should it be desirable that, after the complete filling and hardening of the mortar, said cavity can, if appropriate, be opened again (for example, in order to carry out maintenance operations on cables or pipelines which it contains), it is advantageous that said mortar has a low compressive strength so that it can easily be eliminated. For this purpose, it is possible to use a limited cement dosage, for example in the order of 100 kg/m³, a water/cement ratio in the order of 2, only sand (maximum granulometry 4 mm) and a powerful air entrainer additive making it possible to obtain an air content in the order of 15%-25% of the total volume.

Moreover, it is advantageous that the fluidity of said third flux is sufficiently high, this being achieved with the above formulation, so that the mixture of mortar and of setting and hardening accelerator of which it consists is self-placing, that is to say it flows freely into said cavity, at the same time coating the walls of the latter completely, and also the possible objects located there, and filling the entire volume of said cavity, without leaving any appreciable voids.

If appropriate, colored pigments may be added to at least one of said fluxes in order to color the accelerated mortar in the mass. It is thus possible to indicate the proximity of an object buried in said cavity.

In order to implement the method described above, the present invention relates, furthermore, to a device which is notable in that it comprises:

-   -   a first receptacle for receiving the mortar emerging from said         unloading orifice of said transport vehicle;     -   first means of advance fed with mortar from said first         receptacle and forming said first flux;     -   a second receptacle for receiving said setting and hardening         accelerator;     -   second means of advance fed with setting and hardening         accelerator from said second receptacle and forming said second         flux;     -   means for the amalgamation and mixing of said first and second         fluxes; and     -   third means of advance fed from said amalgamation and mixing         means and forming said third flux of mortar and of setting and         hardening accelerator, resulting from the amalgamation and         mixing of said first and second fluxes.

In an advantageous embodiment, said first and second means of advance, said amalgamation and mixing means and said third means of advance consist of a single endless screw conveyor. This endless screw conveyor may be inclined relative to the horizontal, its lower end being fed with mortar from said first receptacle, its intermediate part being fed with setting and hardening accelerator from said second receptacle, and said third flux of mortar and of setting and hardening accelerator emerging from the side of the upper part of said endless screw conveyor.

It may be advantageous that the device of the invention comprises a third receptacle arranged under the upper part of said endless screw conveyor and intended for receiving said third flux of mortar and of setting and hardening accelerator, and that the lower part of said third receptacle is shaped as a chute capable of introducing said third flux of mortar and of setting and hardening accelerator into said cavity.

In order to facilitate the displacement of the device of the invention from one cavity to another or along an elongate cavity, the first, second and third receptacles and said endless screw conveyor can be carried by a chassis provided with wheels. A cavity filling carriage is thus obtained.

Advantageously, should the cavity to be filled be a trench, said wheels are capable of coming to bear on the ground on either side of said trench, so that the device according to the invention then straddles the latter. In this case, the device may comprise guide means co-operating with said trench and intended for guiding said device along the latter.

Moreover, a plate may be provided, which is integral with said chassis and is capable of functioning as a float for the mortar with accelerated setting and hardening which has just been introduced into said trench. Such a float can bear on the ground on either side of the trench so as to make the level of said mortar flush with that of the ground. Alternatively, it may also penetrate into the trench so as to impart to said mortar a smooth surface set back with respect to the level of the ground.

For filling the trench, the wheeled device can be displaced along said trench, said first receptacle being fed continuously with mortar by said mortar transport vehicle following a road parallel to said trench. In this case, it is advantageous that said wheeled device and said transport vehicle are coupled to a common tractor.

The figures of the accompanying drawing will make it easy to understand how the invention can be implemented. In these figures, identical references designate similar elements.

FIG. 1 is a perspective view of an exemplary embodiment of the device according to the present invention, designed especially for filling trenches of small width.

FIG. 2 is a side elevation view, with partial cutaways, of the device of FIG. 1.

FIG. 3 is a rear elevation view of the device of FIGS. 1 and 2 along the line III-III of FIG. 2.

FIG. 4 is a top view of the device of FIGS. 1, 2 and 3.

FIG. 5 shows a detail of the device of FIGS. 1 to 4 in an enlarged perspective view from above.

FIG. 6 illustrates diagrammatically an alternative embodiment for the device of FIGS. 1 to 4.

FIG. 7 illustrates diagrammatically, in a top view, an example of the implementation of the method according to the present invention for refilling a trench with the device of FIGS. 1 to 4.

The device according to the present invention, and illustrated in FIGS. 1 to 4 and 7, takes the form of a carriage 1 comprising an elongate chassis 2 provided with a pair of front wheels 3 and with a pair of rear wheels 4. In the embodiment illustrated, the two front wheels 3 are mounted in forks 5 freely rotatable and about vertical axes, so that said front wheels 3 are spontaneously orientable (this being especially advantageous in the application illustrated in FIG. 7). By contrast, the two wheels 4 are keyed on their shaft 6 without the possibility of their orientation. Moreover, as is illustrated by broken lines in FIG. 2, the front wheels 3 and/or the rear wheels 4 are mounted so as to be vertically adjustable under the action of jacks, such as that designated by the reference 7 in FIGS. 1 and 2, so that said carriage can occupy either a high displacement position or a low working position.

The carriage 1 is specially designed for the filling of trenches 8 made in the ground 9, and the spacing of the pairs of wheels 3 and 4 is provided so that one wheel of each of the pairs can come to bear on the said ground 9 on one side of said trench 8, the other wheel of each pair coming to bear on the other side of said trench, so that the carriage 1 can be straddled over the latter, as illustrated in FIGS. 1, 3, 4 and 7. The carriage 1 is provided in its front part with coupling means 10.

Mounted on the chassis 2 of the carriage 1 are a hopper 11, a reservoir 12, an endless screw conveyor 13 and a hopper 14.

The endless screw conveyor 13 is inclined relative to the horizontal, with its front part lower than its rear part. The screw of this conveyor 13 is actuated by a motor 50 being arranged in the upper rear part. The hopper 11 is arranged above the front lower part of the endless screw conveyor 13. Said hopper can communicate with the latter by means of an aperture 16 made in this lower part and corresponding with an aperture 17 provided in the casing 18 of the endless screw conveyor 13. The aperture 16 of the hopper 11 can be shut off by means of a door 19 actuated by a mechanism 20.

The reservoir 12 comprises a hopper 21, at the base of which is arranged a screw extractor 22 actuated by a motor 23. The extractor 22 is provided with an outlet conduit 24 issuing into a receptacle 25 arranged above said endless screw conveyor 13 and in communication with the intermediate part of the latter via an aperture 26 formed in said casing 18.

The endless screw conveyor 13 comprises in its upper part a discharge mouth 27 directed downward and arranged above the hopper 14.

The bottom of the hopper 14 is pierced with an oblong aperture 28 delimited laterally by two longitudinal plates 29 and 30 capable of penetrating into said trench 8.

The electrical, hydraulic and/or pneumatic energy necessary for the functioning of the devices of the carriage 1 is delivered to the latter by means of cables or conduits 31 illustrated solely in FIG. 1.

The functioning of the devices of the carriage 1 is controlled from the control panel 32.

The motors 15 and 23 are connected to one another by means of a servo device illustrated diagrammatically by connection 33 in FIG. 2.

The carriage 1 comprises, furthermore, in its front part, a lug 34 capable of penetrating into said trench 8 in order to guide said carriage when it is displaced along the latter, and, in its rear part, a plate 35 covering said trench. When the carriage 1 is in the high position (see the position indicated by dots and dashes in FIG. 2), the lug 34 is disengaged from the trench 8.

FIG. 7 illustrates diagrammatically, in a top view, the use of the carriage 1 for the continuous filling of the trench 8. For this purpose, the carriage 1 is coupled with lateral offset, by means of a chain 36 attached to its coupling means 10, to the rear of the tractor 37 which is displaced in the direction of the arrow F parallel to the trench 8 and which, for example, is capable of depositing a cable 38 into the trench 8. A mixer truck 39 for the transport of ready-to-use mortar is likewise coupled to the tractor 37 by means of a drawbar 40. During the advance of the tractor 37, the mixer 41 of the truck 39 continuously unloads the mortar which it contains into the hopper 11 by means of a chute 42. Said mortar then passes through the aperture 16 and 17 and is driven by the endless screw conveyor 13 in the form of a mortar flux.

Simultaneously, setting and hardening accelerator of the said mortar, the accelerator being held in reserve in the hopper 21, is extracted from the latter by the extractor 22 and falls into said receptacle 25. It passes through the aperture 26 and is driven by the endless screw conveyor 13 in a second flux which is mixed and amalgamated with said first flux, in order to form a third flux of mortar with accelerated setting and hardening, which emerges from the mouth 27 of the endless screw conveyor 13 and pours into the hopper 14. It passes from there into the trench 8 through the oblong funnel formed by the aperture 28 and the plates 29 and 30.

The mortar with accelerated setting and hardening introduced into the trench 8 is floated by the plate 35, in order to obtain a smooth surface 8C for said mortar.

Of course, the rotational speed of the endless screw conveyor 13 is adapted to the speed of advance of the tractor 37, so that the trench 8 is correctly filled with accelerated mortar. By virtue of the servo control 33, the content of setting and hardening accelerator is kept constant at a desired value, whatever the speed of advance.

In an experimental embodiment in which the mixer 41 had a capacity of 6 m³ of mortar, it was possible to fill continuously trenches 8 having a width of 10 to 20 cm and a depth of 30 to 50 cm at a speed of 40 m per minute.

In the above description, it was implicitly assumed that the setting and hardening accelerator took the form of powder. Should said accelerator be slurry, the hopper 21 and the extractor 22, 23 of the reservoir 12 are replaced by a container 43 containing said slurry and by a positive-displacement pump 44 controlled by said servo control 33 and feeding said outlet conduit 24 with slurry (see FIG. 6). 

1. A method for filling a cavity (8) with a mortar capable of setting, at least one setting and hardening accelerator having to be added to said mortar, and said mortar being available at the unloading orifice of a transport vehicle (39) delivering it in the vicinity of said cavity (8), characterized in that a first flux is formed, consisting of said mortar and being displaced in the direction of said cavity (8); a second flux is formed, consisting of said setting and hardening accelerator and being displaced in the direction of said first flux; said second flux is added to said first flux, and said fluxes are mixed in order to amalgamate them into a third flux; and said third flux is introduced by gravity into said cavity (8).
 2. The method as claimed in claim 1, characterized in that the flow rate of said second flux is adjusted as a function of the flow rate of said first flux in order to fix the proportion of setting and hardening accelerator in said third flux.
 3. The method as claimed in either claim 1, characterized in that said mortar is based on Portland cement, while the setting and hardening accelerator is based on calcium aluminates.
 4. The method as claimed in claim 3, characterized in that said Portland cement does not comprise mineral additives, such as fly ash or filler.
 5. The method as claimed in claim 3, characterized in that said setting and hardening accelerator has a C₁₂A₇ content at most equal to 1%.
 6. The method as claimed in claim 1, characterized in that said setting and hardening accelerator takes the form of a powder.
 7. The method as claimed in claim 1, characterized in that said setting and hardening accelerator takes the liquid form of a slurry comprising setting inhibitors of said accelerator and, if appropriate, dispersants.
 8. The method as claimed in claim 3, characterized in that said mortar comprises approximately 100 kg/m³ of cement, a water/cement ratio in the order of 2, only sand with a granulometry at most to 4 mm, and an air entrainer additive making it possible to obtain an air content in the order of 15% to 25% of the total volume.
 9. The method as claimed in claim 1, characterized in that the fluidity of said third flux is sufficiently high to ensure that the mixture of mortar and of setting and hardening accelerator of which it consists is self-placing, that is to say it flows freely into said cavity, at the same time coating the walls of the latter completely, and filling the entire volume of said cavity, without leaving any appreciable voids.
 10. A device for carrying out the method specified under claim 1, characterized in that it comprises: a first receptacle (11) for receiving the mortar emerging from said unloading orifice of said transport vehicle (39); first means of advance (13) fed with mortar from said first receptacle (11) and forming said first flux; a second receptacle (25) for receiving said setting and hardening accelerator; second means of advance (13) fed with setting and hardening accelerator from said second receptacle (25) and forming said second flux; means (13) for adding said second flux to said first flux and for mixing said fluxes, at the same time amalgamating them; and third means of advance (13) fed from said amalgamation and mixing means (13) and forming said third flux of mortar and of setting and hardening accelerator, resulting from the amalgamation and mixing of said first and second fluxes.
 11. The device as claimed in claim 10, characterized in that said first and second means of advance, said amalgamation and mixing means and said third means of advance consist of a single endless screw conveyor (13).
 12. The device as claimed in claim 11, characterized in that said endless screw conveyor (13) is inclined relative to the horizontal, in that its lower end is fed with mortar from said first receptacle (11), in that its intermediate part is fed with setting and hardening accelerator from said second receptacle (25), and in that said third flux of mortar and of setting and hardening accelerator emerges from the side of the upper part of said endless screw conveyor (13).
 13. The device as claimed in claim 12, characterized in that it comprises a third receptacle (14) arranged under the upper part of said endless screw conveyor (13) and intended for receiving said third flux of mortar and of setting and hardening accelerator, and in that the lower part of said third receptacle is shaped as a chute (28, 29, 30) capable of introducing said third flux of mortar and of setting and hardening accelerator into said cavity (8).
 14. The device as claimed in claim 10, characterized in that the first, second and, if appropriate, third receptacles and also said first, second, third means of advance and said amalgamation and mixing means are carried by a chassis (2) provided with wheels (3, 4).
 15. The device as claimed in claim 14, intended for filling a trench (8) made in the ground (9), characterized in that said wheels (3, 4) are capable of coming to bear on the ground on either side of said trench (8).
 16. The device as claimed in claim 15, characterized in that it comprises means (34) for guidance along said trench.
 17. The device as claimed in claim 15, characterized in that it comprises a plate (35) integral with said chassis (2) and capable of functioning as a float.
 18. The method as claimed in claim 1 for filling a cavity taking the form of a trench (8) made in the ground (9), said filling being carried out by means of the device (1) of one of claims 14 to 17, characterized in that said device (1) is displaced along said trench (8), and in that said first receptacle (11) is fed continuously with mortar by said transport vehicle (39) following a road parallel to said trench.
 19. The method as claimed in claim 18, characterized in that said device (1) and said transport vehicle (39) are coupled to a common tractor (37). 